Methods and apparatus for packaging electronic components

ABSTRACT

Packages for elements, e.g., OLEDs, that are temperature sensitive are provided. The packages have a first glass substrate ( 12 ), a second glass substrate ( 16 ), and a wall ( 14 ) that separates the first and second substrates ( 12,16 ) and hermetically seals at least one temperature sensitive element ( 18,28,36 ) between the substrates ( 12,16 ). The wall ( 14 ) comprises a sintered frit and at least a portion of the wall is laser sealed to the second substrate ( 16 ) by melting a glass component of the sintered frit. The minimum width ( 40 ) of the laser-sealed portion of the wall ( 14 ) at any location along the wall ( 14 ) is greater than or equal to 2 millimeters so as to provide greater hermeticity and strength to the package. The laser sealing is performed without substantially degrading the temperature sensitive element(s) ( 18,28,36 ) housed in the package.

I. FIELD OF THE INVENTION

This invention relates to methods and apparatus for packaging electroniccomponents, such as the organic light emitting diodes (OLEDs) used indisplay devices.

II. BACKGROUND OF THE INVENTION

OLED-based displays are currently being considered for use in manyapplications which presently employ liquid crystal displays (LCDs).OLED-based displays can provide brighter and clearer images than liquidcrystal displays and also need less power. However, OLEDs aresusceptible to damage resulting from exposure to oxygen and moisture.Such exposure may lead to a reduction in the useful life of the lightemitting device. Therefore, hermetic sealing is one of basicrequirements for long term performance of OLEDs.

Efforts have been made to hermetically seal OLED-based displays withorganic materials, such as epoxy resins. An alternate technology withsubstantially better performance has been developed by CorningIncorporated, the assignee of this application. In accordance with thisapproach, a frit-containing paste is made by mixing glass particles,filler particles, e.g., crystalline particles, and a vehicle, e.g., avehicle comprising one or more solvents and one or more binders and/ordispersing aids. The paste is dispensed on a first substrate (e.g., afirst glass sheet) and is sintered using, for example, a hightemperature furnace to produce a sintered frit pattern.

The resulting assembly, known as a frit cover glass or simply a cover,is combined with a second substrate (e.g., a second glass sheet)carrying one or more OLED devices. The cover and the second substrateare sealed together by exposing the sintered frit pattern to laserenergy. In particular, a laser beam is scanned (traversed) over thesintered frit pattern to locally raise the temperature of the sinteredfrit above its softening point. In this way, the sintered frit adheresto the second substrate and forms a strong seal between the cover andthe second substrate. Since the sintered frit is a glass and ceramicmaterial, as opposed to an organic material, the penetration of oxygenand moisture through the frit seal is much slower than through the epoxyseals previously used to encapsulate OLED devices.

The sealing of larger size OLED devices, such as full-size TVs having adiagonal of, for example, 14 inches or larger, is more challenging thansealing smaller OLED devices, such as those used in cell phones, PDAsand other mobile electronic devices. For a typical small OLED device, asintered frit with a sealing width of around 0.7-1.0 mm has provedsufficient. In particular, these sealing widths have been found toprovide a sufficient moisture and oxygen barrier to allow a typicaldisplay to operate successfully for 1-3 years. In addition, such sealingwidths provide sufficient mechanical strength for these smaller devices.The small sealing widths are also compatible with the limited spaceavailable on small OLED devices for sealing. For example, for a typicalsmall OLED device, the edge area that can be dedicated to sealing has awidth of only 1.0-1.5 millimeters.

In comparison to small devices, larger size OLED devices such as TVsrequire longer service times and have more demanding mechanicalrequirements. As a consequence, a need has arisen for large sizepackages for sensitive electronic components, such as OLEDs, which haveseals that are stronger and/or provide greater protection from influx ofwater and oxygen. The present invention addresses this need.

III. SUMMARY OF THE INVENTION

In accordance with a first aspect, the invention provides a packagingmethod comprising:

(A) providing a first substrate (12), a second substrate (16), a wall(14) that separates the first and second substrates (12,16), and atleast one temperature sensitive element (18,28,36) that is disposedbetween the first and second substrates (12,16), said wall (14)comprising a sintered glass frit having a melting temperatureT_(frit-melt) and said at least one temperature sensitive element(18,28,36) having a degradation temperature T_(degrade), said wall (14)being bonded to said first substrate (12) and in contact with saidsecond substrate (16);

(B) impinging a laser beam having a diameter D_(beam) on the wall (14);and

(C) traversing the beam along a length of the wall (14) at a speed S toheat the wall (14) and seal at least a portion of the width (42) of thewall (14) to the second substrate (16);

wherein:

(i) the minimum distance (44) between an edge of the at least onetemperature sensitive element (18,28,36) and an edge of the portion ofthe wall (14) sealed to the second substrate (16) at any location alongthe wall is L_(min);

(ii) the minimum width (40) of the portion of the wall (14) sealed tothe second substrate (16) at any location along the wall isW_(seal-min); and

(iii) D_(beam), L_(min), W_(seal-min), T_(frit-melt), T_(degrade), and Ssatisfy the relationships:

W_(seal-min)≧2 mm,   (a)

D_(beam)>W_(seal-min),   (b)

S≧(11 mm/sec)·(D _(beam)/2 mm)·(0.2 mm/L_(min))·(65° C./T _(degrade))²,  (c)

and

S≦(130 mm/sec)·(D _(beam)/2 mm)·(450° C./T _(frit-melt))².   (d)

In accordance with a second aspect, the invention provides a packagecomprising a first glass substrate (12), a second glass substrate (16),a wall (14) that separates the first and second substrates (12,16), andat least one element (18,28,36) that is sensitive to oxygen and/ormoisture and is hermetically sealed between the first and secondsubstrates (12,16) by the wall (14), said wall (14) comprising asintered glass frit having a melting temperature T_(frit-melt) and saidat least one element (18,28,36) having a degradation temperatureT_(degrade), wherein:

(i) at least a portion of the width (42) of the wall (14) is lasersealed to the second substrate (16);

(ii) the minimum width (40) of the portion of the wall (14) sealed tothe second substrate (16) at any location along the wall isW_(seal-min);

(iii) the minimum distance (44) between an edge of the at least oneelement (18,28,36) and an edge of the portion of the wall (14) sealed tothe second substrate (16) at any location along the wall is L_(min); and

(iv) W_(seal-min), L_(min), and T_(frit-melt) satisfy the relationships:

W_(seal-min)≧2 mm;   (a)

0.2 mm≦L_(min)≦2.0 mm; and   (b)

T _(frit-melt)≧6.0·T _(degrade).   (d)

In certain embodiments of the first and second aspects of the invention,W_(seal-min) is less than or equal to 7 millimeters. Preferably,W_(seal-min) is less than or equal to 6 millimeters and greater than orequal to 3 millimeters, e.g., W_(seal-min) approximately equals 5millimeters.

In accordance with a third aspect, the invention provides a packagecomprising a first glass substrate (12), a second glass substrate (16),a wall (14) that comprises a sintered glass frit and separates the firstand second substrates (12,16), and at least one element (18,28,36) thatis sensitive to oxygen and/or moisture and is hermetically sealedbetween the first and second substrates (12,16) by the wall (14),wherein the wall (14) comprises a plurality of isolated compartments(32), each compartment (32) comprising a plurality of sub-walls (30)which are arranged so that oxygen and/or moisture can readily passthrough the compartment only if at least two of the sub-walls (30) arebreached.

In accordance with a fourth aspect, the invention provides a packagecomprising a first glass substrate (12), a second glass substrate (16),a wall (14) that separates the first and second substrates (12,16), andat least one element (18,28,36) that is sensitive to oxygen and/ormoisture and is hermetically sealed between the first and secondsubstrates (12,16) by the wall (14), wherein the wall (14) comprises aplurality of sub-walls (30) that comprise a sintered glass frit and asub-wall (34) that (i) comprises an organic material, e.g., an epoxyresin, and (ii) is located between two of the sub-walls that comprise asintered frit. In certain embodiments, the sub-wall that comprises anorganic material does not contact the sub-walls that comprise a sinteredglass frit.

The reference numbers used in the above summaries of the various aspectsof the invention are only for the convenience of the reader and are notintended to and should not be interpreted as limiting the scope of theinvention. More generally, it is to be understood that both theforegoing general description and the following detailed description aremerely exemplary of the invention and are intended to provide anoverview or framework for understanding the nature and character of theinvention.

Additional features and advantages of the invention are set forth in thedetailed description which follows, and in part will be readily apparentto those skilled in the art from that description or recognized bypracticing the invention as described herein. The accompanying drawingsare included to provide a further understanding of the invention, andare incorporated in and constitute a part of this specification. It isto be understood that the various features of the invention disclosed inthis specification and in the drawings can be used in any and allcombinations.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, cross sectional, side view of a display deviceaccording to an embodiment of the present invention.

FIG. 2 is a cross sectional side view of a glass sheet with a sinteredfrit pattern bonded thereto in accordance with an embodiment of thepresent invention.

FIG. 3 is a top view of the glass sheet of FIG. 2 showing the sinteredfrit pattern as having the shape of a frame.

FIG. 4 is a schematic diagram showing various geometric relationshipsrelevant to the present invention.

FIG. 5A is a plot showing the relationship between laser power and laserscanning speed for three different sintered frit widths. The verticalaxis in this figure is laser power in watts and the horizontal axis isscanning velocity in millimeters/second.

FIG. 5B is a plot showing the relationship between laser power andsintered frit width for four different laser scanning speeds. Thevertical axis in this figure is laser power in watts and the horizontalaxis is sintered frit width in millimeters.

FIG. 6 is a schematic diagram illustrating a thermal management systemthat can be used in connection with certain embodiments of the presentinvention.

FIG. 7 is a schematic diagram of an embodiment of the inventionemploying a single sintered frit wall.

FIG. 8 is a schematic diagram of an embodiment of the inventionemploying a sintered frit wall composed of nested sub-walls.

FIG. 9 is a schematic diagram of an embodiment of the inventionemploying a wall comprising nested sub-walls composed of a sintered fritand a sub-wall composed of an organic material.

FIG. 10 is a schematic diagram of an embodiment of the inventionemploying a wall having isolated compartments which can mitigate leakingdue to a local defect.

V. DETAILED DESCRIPTION OF THE INVENTION AND ITS PREFERRED EMBODIMENTS

As discussed above, in accordance with certain of its aspects, thepresent invention relates to packaging of temperature sensitiveelements, e.g., OLEDs, by laser sealing wherein the resulting seal has awider width (i.e., a larger W_(seal-min)) so as to provide the packagewith greater strength and a longer useful life.

FIG. 1 is a schematic, cross-sectional, side view of a hermeticallysealed OLED display device, generally designated by reference numeral10, comprising a first substrate 12, a sintered frit pattern 14, asecond substrate 16, at least one OLED element 18, and at least oneelectrode 20 in electrical contact with the OLED element. Typically,OLED element 18 is in electrical contact with an anode electrode and acathode electrode. Electrode 20 in FIG. 1 is intended to representeither electrode. Although only a single OLED element is shown forsimplicity, display device 10 may have many OLED elements disposedtherein. The typical OLED element 18 includes one or more organic layers(not shown) and anode/cathode electrodes. However, it should be readilyappreciated by those skilled in the art that any known OLED element 18or future OLED element 18 can be used in display device 10. In addition,it should be appreciated that another type of thin film device can behoused in the packages of the invention besides OLED element 18. Forexample, thin film sensors, photovoltaic cells, and the like may befabricated using the present invention.

In one embodiment, first substrate 12 is a transparent, thin glass sheetproduced using the fusion process, e.g., Corning Incorporated's Code1737, EAGLE²⁰⁰⁰® or EAGLE XG™ glasses, or the fusion glasses produced byNippon Electric Glass Co., NHTechno, and Samsung Corning Precision GlassCo. Alternatively, first substrate 12 can be produced by otherprocesses, e.g., the float process used by Asahi Glass Co. to produceOA10 glass and OA21 glass. Second substrate 16 may be made of the sameglass as first substrate 12 or it may be a non-transparent substrate.

Prior to sealing first substrate 12 to second substrate 16, afrit-containing paste is deposited on a major surface of first substrate12 in a predetermined pattern, which is typically placed approximately 1mm away from the free edges 13 of first substrate 12 as a line, or aplurality of connected lines, and is typically deposited in the shape ofa closed frame or wall. As used herein, the word “wall” is used in thesense of a barrier between the inside of the package and the outsideatmosphere. As such, it can have a variety of shapes, e.g., circular,square, rectangular, triangular, etc. As will be discussed below, incertain embodiments of the invention, the wall can be composed ofsub-walls (see FIGS. 8-10).

Preferably, after being deposited on first substrate 12, thefrit-containing paste is sintered prior to being sealed to secondsubstrate 16. To accomplish this, the deposited paste can, for example,be heated so that it becomes attached to first substrate 12, and thenthe substrate/heated paste combination can be placed in a furnace whichsinters the paste (also referred to in the art as “firing” or“consolidating” the paste) to form the desired assembly of sintered fritpattern 14 bonded to first substrate 12. Alternatively, the initialheating step can be omitted, with the substrate/paste patterncombination being directly placed into a furnace for sintering. As astill further alternative, the sintering can be performed by heatingjust the paste pattern and the surrounding substrate, rather than theentire glass sheet. This localized heating can be performed on theentire paste pattern simultaneously or on sequential portions. Ingeneral, the furnace approach with an initial heating step is preferredsince during the initial heating, organic components of the vehicle,e.g., organic binder materials, are burned out. The sinteringtemperature and time will, of course, depend on the composition of thepaste, specifically, the composition of the paste's glass particles.

After sintered frit pattern 14 is formed, it can be ground, if necessaryand desired, so that the height variation along the frit line does notexceed about 2-4 microns, with a typical target height H being 10microns to greater than 20 microns, depending on the application fordevice 10; however, more typically height H is about 14-16 microns. Ifthe height variation is larger, a gap, which may be formed between thesintered frit pattern and second substrate 16 when glass sheet 12 andsubstrate 16 are joined, may not close when the sintered frit pattern 14melts during laser sealing (see below), or the gap may introducestresses which can crack one or both of the substrates, particularlyduring cooling. An adequate but not overly thick frit height H allowsthe laser sealing to be performed from the backside of first substrate12. If sintered frit pattern 14 is too thin, it does not leave enoughmaterial to absorb the laser radiation, resulting in failure. If thepattern is too thick, it will be able to absorb enough energy at thesurface of the first substrate to melt, but will prevent the necessaryenergy needed to melt the sintered frit from reaching the region of thefrit proximate substrate 16. This usually results in poor or spottybonding of the first and second substrates.

If the sintered frit pattern 14 is ground, the assembly of firstsubstrate 12 and its attached sintered frit pattern 14 may go through amild ultrasonic cleaning environment to remove any debris that may haveaccumulated. During cleaning, the temperature can be kept low to avoiddegradation of the sintered frit pattern 14. After cleaning (ifperformed), a final processing step can be performed to remove residualmoisture. For example, the assembly can be placed in a vacuum oven at atemperature of 100° C. for 6 or more hours. After removal from the oven,the assembly can be placed in a clean room box to deter accumulation ofdust and debris.

The sealing process includes placing the assembly of first substrate 12and sintered frit pattern 14 on top of substrate 16, with one or moreOLEDs 18 and one or more electrodes 20 deposited on the substrate 16, insuch a manner that the sintered frit pattern, the one or more OLEDs, andthe electrodes are sandwiched between the first and second substrates 12and 16 separated by the thickness of the frit pattern. Mild pressure canbe applied to the first and second substrates 16 to keep them in contactduring the sealing process.

A laser beam is then directed onto frit pattern 14 through firstsubstrate 12. Alternatively, if substrate 16 is transparent at thesealing wavelength, sealing may be performed through substrate 16, orthrough both substrates. In each case, the beam or beams are traversedover the sintered frit pattern to locally heat the pattern such that theglass component of the sintered frit melts and forms a hermetic sealwhich connects and bonds substrate 12 to substrate 16. The gap betweensubstrates 12 and 16 resulting from the presence of the sintered fritseal 14 forms a hermetic envelope or package for OLED element 18. Inparticular, the package comprises the two substrates which form thefaces of the package and the sintered frit 14 which forms the wall ofthe package. The hermetic seal of the package protects OLED(s) 18 bypreventing oxygen and moisture in the ambient environment from enteringinto OLED display 10.

The laser beam or beams used during bonding can be defocused, forexample, to make the temperature gradient within the sintered fritpattern more gradual. It should be noted that if the gradient is toosteep (focus is too tight), OLED display 10 may exhibit cracking andsubsequent failure. The sintered frit pattern generally needs a warm upand cool down phase during melting. In addition, prior to use, theassembly of the first substrate 12 and sintered frit pattern 14 ispreferably stored in an inert atmosphere to prevent re-adsorption of O₂and H₂O before melting.

Further details regarding the formation of hermetically-sealed packagesby traversing a laser beam over a sintered frit pattern can be found incommonly-assigned U.S. Patent Application Publications Nos.2006/0082298, 2007/0128965, 2007/0128966, and 2007/0128967, the contentsof which in their entireties are incorporated herein by reference.

Similarly, suitable compositions for the sintered glass frit which formsthe wall of the package can be found in commonly-assigned U.S. PatentApplication Publication No. 2005/0001545, entitled “Glass Package thatis Hermetically Sealed with a Frit and Method of Fabrication,” which isa continuation-in-part of U.S. Pat. No. 6,998,776, the contents of bothof which in their entirety are incorporated herein by reference. Apresently preferred glass for the glass component of the sintered fritcomprises: 22.92 mole % Sb₂O₃, 46.10 mole % V₂O₅, 0.97 mole % TiO₂, 0.97mole % Al₂O₃, 2.61 mole % Fe₂O₃, and 26.43 mole P₂O₅; a presentlypreferred ceramic for the filler particles of the sintered fritcomprises: 50 mole % SiO₂, 25 mole % Al₂O₃, and 25 mole % Li₂O. Othersintered glass frits, now known or subsequently developed, can, ofcourse, be used in the practice of the invention.

As discussed above, large size displays, i.e., displays having adiagonal of at least 14 inches, present challenges to the existingprocesses for sealing OLEDs. Larger displays have longer seal lengthswhich means that there are more chances for water and oxygen topenetrate through the barrier provided by the seal. Importantly, OLEDdisplay degradation does not happen uniformly over all of the displayarea, but primarily next to leak locations. Therefore, the degradationrate of an OLED display is about the same as the area next to leaklocations, which is the seal perimeter. Larger OLED devices have largerseal perimeters. In particular, for typical display aspect ratios, theratio of the display area to its perimeter is proportional to thedisplay size.

One way to decrease water and oxygen permeability rates is to increasethe width of the seal. In general terms, the permeability rate scalesexponentially with seal width for a seal composed of a sintered glassfrit. Thus, given that the lifetime of a small OLED, e.g., an OLED foruse in a cell phone, is on the order of 1-2 years with a 0.7-1.0 mm sealwidth, then the lifetime of a device having a sintered frit whoseminimum seal width is 5 mm will be on the order of about 50 years.Moreover, the wider sealing width will also improve the overallmechanical strength of the device.

One approach for increasing the effective width of a sintered frit sealis to use a wall composed of multiple sub-walls nested within oneanother (see, for example, FIGS. 8-10, where reference number 14represents the wall and reference number 30 represents sintered glassfrit sub-walls). The sub-walls can, for example, have a width in thepreviously used 0.7-1.0 mm range. The presence of these multiplesub-walls increases both the hermeticity of the package and itsstrength.

Unfortunately, in connection with the present invention, it wasdiscovered that multiple sintered-frit sub-walls in and of themselvespresent significant sealing challenges. Specifically, it was found thatalthough one of the sub-walls could be laser sealed using the techniquesemployed with small OLED packages, when laser sealing was performed onanother sub-wall, the heat generated by the laser damaged the seal ofthe first sub-wall. In particular, sealing of the second sub-wall wasfound to delaminate the neighboring first sub-wall, probably as theresult of thermal expansion. Thus, in terms of laser sealing, it wasdiscovered that a nested set of sintered-frit sub-walls need to betreated as one thick wall with all of the sub-walls being sealedtogether at one time.

FIG. 4 is a schematic diagram showing various geometric relationshipsrelevant to the present invention. In this figure, reference number 36represents a temperature sensitive element, e.g., an OLED, and referencenumber 14 represents the wall of the assembled package for thetemperature sensitive element. Wall 14 can be 1) a single sintered glassfrit (see, for example, FIGS. 1 and 7), 2) a plurality of sintered-fritsub-walls (see, for example, FIGS. 8 and 10 where the sintered-fritsub-walls are identified by the reference number 30), or 3) acombination of sintered-frit sub-walls and one or more additionalsub-walls composed of an organic material, e.g., an epoxy resin (see,for example, FIG. 9 where the sintered-frit sub-walls are identified bythe reference number 30 and the sub-wall composed of an organic materialis identified by the reference number 34).

In FIG. 4, the overall width of wall 14 is illustrated by line 42 andthe sealed width is illustrated by line 40, where the sealed width isthe portion of the wall which becomes laser sealed to the secondsubstrate. As shown in FIG. 4, wall 14 does not include sub-walls. Ifsub-walls are used, the overall width is simply the distance between theinnermost edge of the innermost sub-wall and the outermost edge of theoutermost sub-wall and the sealed width is the distance between theinnermost and outermost locations where the wall becomes laser sealed tothe second substrate.

Sealed width 40 can be equal to overall width 42 or, as shown in FIG. 4,smaller than the overall width so as to leave unsealed portions 38.Also, the sealed width can be uniform, as shown in FIG. 4, or can varyalong the length of the wall. In either case, the sealed width ischaracterized by a minimum value, i.e., W_(seal-min). For the uniformsealed width case illustrated in FIG. 4, W_(seal-min) is equal to thelength of line 40; for the general case, W_(seal-min) is the smallesttransverse width of the sealed portion of the wall at any place alongthe length of the wall.

FIG. 4 also shows the spatial relationship between the temperaturesensitive component 36 and the wall 14. In particular, reference number44 shows the minimum distance L_(min) between an edge of the temperaturesensitive element and an edge of the portion of the wall sealed to thesecond substrate. As shown in FIG. 4, the spacing between thetemperature sensitive element and the sealed portion of the wall isconstant, it being understood that this spacing may be different atdifferent locations along the wall depending on the configuration of thewall and the layout of the temperature sensitive element or elementswithin the package defined by the wall. For cases in which the spacingvaries, L_(min) is smallest spacing anywhere along the length of thewall.

In connection with the laser sealing of sintered glass frits havingwidths in the 0.7-1.0 mm range, certain combinations of laser power andsealing speed have been found acceptable. For example, a laser beam witha Gaussian intensity distribution has been found suitable, provided thebeam diameter is 1.8 times the width of the sintered glass frit. For the0.7-1.0 mm sintered-frits, this relationship provides a uniformtemperature distribution across the sintered frit and effectiveheating/cooling rates along the sintered frit. (It should be noted thatas used herein, beam diameter (D_(beam)) is determined using the 1/e²definition of beam size of the ISO 11146 standard. That is, theboundaries of the laser beam are defined as the locations at which beamintensity has fallen to 1/e² of its peak value.)

With larger beam diameters and larger sintered-frit widths, the amountof time each individual location in the longitudinal direction is heatedchanges significantly. In particular, to have the same linear heatingrate, a larger laser spot size requires a higher scanning speed. Lookedat another way, sealing at the same scanning speed for a 1.8 mm beamsize and a 9 mm beam size would mean effectively decreasing the linearheating rate by 5 times. These considerations suggest that a sealed fritwidth of 5 mm would require a laser spot size of 9 mm with significantlyhigher power and sealing speed ˜5 times faster than that for 1 mm fritwith 1.8 mm spot size.

More generally, a change in the width of the sealed wall changes powerrequirements for the laser, scanning speed, and most importantly thermalmanagement, since the amount of heat supplied to the package incomparison to a thinner wall becomes much larger. In addition, changesin beam shape also become relevant in reducing the adverse effects ofthe sealing process on the temperature sensitive element(s) beingpackaged.

In general, speed and power are linked since the temperature required tomelt the sintered-frit and thus form a seal with the second substrate isthe same regardless of power and speed. However, at lower speeds moreheat diffusion occurs, leading to a wider heated area in the glass andthus a greater possibility of damage to the temperature sensitiveelement(s) which are being packaged.

FIGS. 5A and 5B show the results of experiments and calculationsperformed with different beam sizes and sintered-frit widths todetermine the relationship between laser power and laser scanning speed.In FIG. 5A the horizontal axis is scanning speed in millimeters/secondand the vertical axis is laser power in watts required to heat the fritto its melting temperature; in FIG. 5B the horizontal axis issintered-frit width in millimeters and the vertical axis is again laserpower in watts required to heat the frit to its melting temperature. InFIG. 5B, the plotted values for sintered-frit widths greater than 5millimeters and powers greater than 800 watts are calculated valuesbased on the measurements obtained for the smaller widths and lowerpowers.

FIG. 5B also includes horizontal line 22 and vertical line 24.Horizontal line 22 represents a practical upper limit on laser powerbased on the power of lasers that are currently commercially available,i.e., a laser power in the range of 3000-4000 watts. Although available,such high power lasers are expensive and thus in terms of costeffectiveness, lasers having a power that is less than or equal to 1000watts are preferred. Vertical line 24 shows that when this criterion isapplied, the width of the sintered-frit which is being laser sealed ispreferably less than about 7 millimeters.

In view of the foregoing, it can be seen that larger sintered-fritwidths need higher laser powers and faster scanning speeds. Inparticular, sealing larger sintered-frit widths require faster scanningspeeds to avoid thermal stress in the glass, as well as damage totemperature sensitive element(s) within the package.

In general terms, the local temperature during laser sealing scaleslinearly with power density and speed to the power 0.5. Experimentally,it has been found that a Gaussian-shaped beam with a diameter at least1.5 (preferably, at least 1.8) times larger than the sintered-frit widthgives a good quality, uniform seal, provided the temperatures achievedat the center and the edge of the sintered-frit are high enough to meltthe glass component of the sintered frit. For a 5 mm frit, this resultsin a 9 mm Gaussian beam. For other beam shapes, the beam width can besimilarly determined.

For example, a Gaussian beam can be converted into a flat top beam usingbeam shaping equipment, e.g., a Newport refractive beam shaper, CatalogNumber GBS-NIR-H (Newport Corporation, Irvine, Calif.). For a 9 mmGaussian beam and a 5 mm sintered frit, the ratio of the temperature atthe center of the sintered frit to the temperature at its edge can beestimated as:

T_(edge)/T_(center)˜P_(center)/P_(edge)*(a_(center)/a_(edge))^(0.5).

For the above parameters, T_(edge)/T_(center) for a Gaussian beam isequal to 0.48 and this has been found to give a good quality seal. Inthe case of a flat top beam, P_(center)=P_(edge). As a result, the beamdiameter can be significantly smaller, e.g., a_(center)/a_(edge) can beapproximately 1.15. This means that for round flat top beam, the beamdiameter only needs to be 1.05 (preferably, 1.15-1.2) times larger thanthe width of the sintered-frit. This is a significant savings in powerfor the same power density as a Gaussian beam.

The above relationship can also be derived using the following, somewhatmore general, relationship:

T_(edge)/T_(center)˜(P_(center)/P_(edge))(D_(beam)/a)^(0.5)(F(Dg,Df,h)),

where, as above, P is power density, D_(beam) is beam diameter, a islength of the segment of the beam diameter at the frit edge, andF(Dg,Df,h) is a diffusion function, where Dg is thermal diffusivity forthe glass substrate, Df is thermal diffusivity for the sintered frit,and h is frit width. In the case of a Gaussian beam with a diameter of 9mm and a sintered frit width of 5 mm, the above relationship gives anestimate for T_(edge) as 0.6-0.7 of T_(center).

In the case of a flat top beam, F(Df,Dg,h) will be about the same as fora Gaussian beam. D_(beam)a needs to be about 2, meaning that the beamdiameter for the flat top beam can be reduced to D_(beam)h=1.05(preferably, 1.15) instead of D_(beam)/h=1.5 (preferably, 1.8) for aGaussian beam.

As indicated above, for wider sintered-frits, the requirements for alarger beam diameter and the same linear speed of frit exposure meanthat higher power densities and faster translation speeds need to beused. A relationship between translation speed (scanning speed) andother parameters of the system can be obtained as follows.

In order to obtain a good seal without generating excessive heat damage,the following relationship is preferably satisfied:

K1*T _(frit)(edge)<τ^(0.5) <K2*T _(glass)(x),

where τ is exposure time, K1 and K2 are scaling coefficients, whichdepend on the laser power density and its distribution, T_(frit)(edge)is the temperature of the sintered frit at its edge needed to achievemelting, and T_(glass)(x) is the temperature of the glass substrate at adistance x from the edge of the sintered frit which needs to be lowenough so as not to damage the temperature sensitive element(s) beingpackaged. As expressed in this relationship, the exposure time of thefrit by the laser needs to be long enough to melt the frit all the waythrough its thickness, and short enough so that the glass at a distancex from edge of the sintered frit does not get too hot.

Typical values are T_(frit)(edge)>450° C., T_(glass)(x=0.2 mm)<85° C.(i.e., a delta T from room temperature equal to 65° C.). The exposuretime is simply related to the diameter of the beam τ=D_(beam)/S, whereD_(beam) is the beam diameter and S is the scanning speed of the laserover the sintered frit. In order for a 15 micron frit to be meltedthroughout its height, τ needs to greater than about 15 milliseconds(preferably, 25 milliseconds, which corresponds to a scanning speed of75 mm/s for a 2 mm beam diameter). To keep the glass cool enough atx>0.2 mm, τ needs to be smaller than 180 milliseconds. This gives arange at any given beam diameter for the speed requirements. This rangeis applicable to various systems since the thermal diffusivity of atypical sintered frit and a typical glass substrate will have the sameorder of magnitude and the frit thickness, e.g., 15-20 microns, can beexpected to be smaller than the distance of the heat sensitive elementfrom the edge of the sintered frit (e.g., 200 um).

Using the above relationship, one can determine that to seal a 5 mm fritwith a 9 mm beam diameter, the speed needs to be slower than 360 mm/sand faster than 50 mm/s, while for a 3 mm frit with 5.4 mm spot size,the speed range is 216 to 30 mm/s.

The relationship between the scanning speed S and the parameters of thesystem can be further quantified by explicitly including in the speeddetermination the distance between the edge of the sealed portion of thefrit and the temperature sensitive element, the degradation temperatureof that element, and the melting temperature of the sintered frit. Whenthat is done, the following relationships are obtained:

S≧(11 mm/sec)·(D _(beam)/2 mm)·(0.2 mm/L _(min))·(65° C./T _(degrade))²,and

S≦(130 mm/sec)·(D _(beam)/2 mm)·(450° C./T _(frit-melt))².

Preferably,

S≦(80 mm/sec)·(D _(beam)/2 mm)·(450° C./T _(frit-melt))².

As shown in FIG. 5, higher speeds require higher laser powers in orderto reach the same temperature at the sintered frit. The relationshipbetween power density P and scanning speed S at the same spot size canbe written:

P/(S)^(0.5)=constant.

From this relationship, it can be seen that an increase in speed byfactor of 4 requires an increase in P by factor of 2.

As can be seen, the above relationships for S take into account thedegradation temperature of the one or more elements, e.g., OLEDs, beingpackaged. To further reduce the chances of thermal damage, it can bebeneficial to use thermal sinking for first and second substrates. Anexample of such thermal sinking is shown in FIG. 6 where, for example,plate 26 can be composed of aluminum and plate 24 can be composed ofsilica. Similarly, it is preferable to mask the laser beam so that onlythe portion needed to heat the wall 14 reaches the package.

Turning to FIGS. 7-10, these figures illustrate various constructionsfor the wall of the package. In these figures, the reference number 28represents the one or more temperature sensitive elements, e.g., OLEDsbeing housed in the package.

FIG. 7 shows the approach in which a single thick wall is used toprovide the hermetic seal. FIG. 8 shows an alternate approach whereinthe overall width of the wall is still thick but rather than achievingthe thickness through the use of a single wall, multiple sub-walls,e.g., two sub-walls as illustrated in FIG. 8, are used.

FIG. 9 shows a further approach in which sub-walls composed of asintered glass frit are used in combination with a sub-wall composed ofan organic material. The organic material is preferably an epoxy resinbut other materials, such as a UV curable acrylic resin, can be used inthe practice of this aspect of the invention. The sub-wall composed ofan organic material is preferably sandwiched between sub-walls composedof a sintered glass frit as shown in FIG. 9, but other arrangements canbe used if desired, e.g., the sub-wall composed of an organic materialcan be the innermost or outermost sub-wall. Also, although the use of asingle sub-wall composed of an organic material is shown in FIG. 9,multiple sub-walls of this type can be used if desired. When a sub-wallcomposed of an organic material is used, the laser beam used to seal thesub-walls composed of the sintered glass frit should be masked so thatit does not impinge on the organic material.

FIG. 10 shows a wall which includes multiple sub-walls 30 arranged toform isolated compartments 32. In this way, oxygen and/or moisture canreadily pass through one of the compartments only if at least two of thesub-walls of that compartment are breached. Other configurations besidesthe one shown in FIG. 10 can be used in the practice of this aspect ofthe invention. For example, the angled sub-walls can intersect theparallel sub-walls at 90°, thus forming a ladder-like or honeycomb-typestructure along the length of wall. Also, rather than a single layer ofisolated compartments, multiple layers can be used to provide evengreater protection against localized failures of the wall.

From the foregoing it can be seen that the preferred embodiments of thevarious aspects of the invention provide a number of benefits including:longer product lifetimes due to lower rates of moisture and oxygenpermeation, higher mechanical strength since strength is related to thewidth of the sealed frit, and/or combinations of sintered frit andorganic seals to provide both a hermetic barrier and high mechanicalstrength.

A variety of modifications which do not depart from the scope and spiritof the invention will be evident to persons of ordinary skill in the artfrom the foregoing disclosure. As just one example, although theinvention has been described in terms of sealing of packages for usewith large OLED-based displays, it can also be used with small displaysor with other types of temperature sensitive elements, if desired. Thefollowing claims are intended to cover the specific embodiments setforth herein as well as such modifications, variations, and equivalents.

1. A packaging method comprising: (A) providing a first substrate, asecond substrate, a wall that separates the first and second substrates,and at least one temperature sensitive element that is disposed betweenthe first and second substrates, said wall comprising a sintered glassfrit having a melting temperature T_(frit-melt) and said at least onetemperature sensitive element having a degradation temperatureT_(degrade), said wall being bonded to said first substrate and incontact with said second substrate; (B) impinging a laser beam having adiameter D_(beam) on the wall; and (C) traversing the beam along alength of the wall at a speed S to heat the wall and seal at least aportion of the width of the wall to the second substrate; wherein: (i)the minimum distance between an edge of the at least one temperaturesensitive element and an edge of the portion of the wall sealed to thesecond substrate at any location along the wall is L_(min); (ii) theminimum width of the portion of the wall sealed to the second substrateat any location along the wall is W_(seal-min); and (iii) D_(beam),L_(min), W_(seal-min), T_(frit-melt), T_(degrade), and S satisfy therelationships:W_(seal-min)≧2 mm,   (a)D_(beam)>W_(seal-min),   (b)S≧(11 mm/sec)·(D _(beam)/2 mm)·(0.2 mm/L _(min))·(65° C./T _(degrade))²,  (c)andS≦(130 mm/sec)·(D _(beam)/2 mm)·(450° C./T _(frit-melt))².   (d)
 2. Themethod of claim 1 wherein:S≦(80 mm/sec)·(D _(beam)/2 mm)·(450° C./T _(frit-melt))².
 3. The methodof claim 1 wherein W_(seal-min)≦7 mm.
 4. The method of claim 1 wherein 3mm≦W_(seal-min)≦6 mm.
 5. The method of claim 1 where W_(seal-min)approximately equals 5 mm.
 6. The method of claim 1 wherein the wallcomprises a plurality of nested sub-walls, each of which comprise thesintered glass frit.
 7. The method of claim 6 wherein the wall comprisesa nested sub-wall which comprises an epoxy resin.
 8. The method of claim1 wherein the wall comprises a plurality of isolated compartments. 9.The method of claim 1 wherein the wall comprises filler particlesembedded in the sintered glass frit.
 10. The method of claim 1 wherein 5mm/sec≦S≦100 mm/sec.
 11. The method of claim 1 wherein the laser beam isa Gaussian beam and D_(beam)/W_(seal-min) is greater than 1.5.
 12. Themethod of claim 1 wherein the laser beam is a flat-top beam andD_(beam)/W_(seal-min) is greater than 1.05.
 13. The method of claim 1wherein the at least one temperature sensitive element is an organiclight emitting diode.
 14. A package comprising a first glass substrate,a second glass substrate, a wall that separates the first and secondsubstrates, and at least one element that is sensitive to oxygen and/ormoisture and is hermetically sealed between the first and secondsubstrates by the wall, said wall comprising a sintered glass frithaving a melting temperature T_(frit-melt) and said at least one elementhaving a degradation temperature T_(degrade), wherein: (i) at least aportion of the width of the wall is laser sealed to the secondsubstrate; (ii) the minimum width of the portion of the wall sealed tothe second substrate at any location along the wall is W_(seal-min);(iii) the minimum distance between an edge of the at least one elementand an edge of the portion of the wall sealed to the second substrate atany location along the wall is L_(min); and (iv) W_(seal-min), L_(min),and T_(frit-melt) satisfy the relationships:W_(seal-min)≧2 mm;   (a)0.2 mm≦L _(min)≦2.0 mm; and   (b)T _(frit-melt)≧6.0·T _(degrade).   (c)
 15. The package of claim 14wherein the at least one temperature sensitive element is an OLED-baseddisplay having a diagonal which is equal to or greater than 14 inches.16. A package comprising a first glass substrate, a second glasssubstrate, a wall that comprises a sintered glass frit and separates thefirst and second substrates, and at least one element that is sensitiveto oxygen and/or moisture and is hermetically sealed between the firstand second substrates by the wall, wherein the wall comprises aplurality of isolated compartments, each compartment comprising aplurality of sub-walls which are arranged so that oxygen and/or moisturecan readily pass through the compartment only if at least two of thesub-walls are breached.
 17. The package of claim 16 wherein the elementis an organic light emitting diode.
 18. A package comprising a firstglass substrate, a second glass substrate, a wall that separates thefirst and second substrates, and at least one element that is sensitiveto oxygen and/or moisture and is hermetically sealed between the firstand second substrates by the wall, wherein the wall comprises aplurality of sub-walls that comprise two sub-walls comprised of sinteredglass frit and a sub-wall that (i) is comprised of an organic materialand (ii) is located between the two sub-walls comprised of a sinteredfrit.
 19. The package of claim 18 wherein the organic material is anepoxy resin.
 20. The package of claim 18 wherein the element is anorganic light emitting diode.